1. Field of the Invention
Embodiments of the present disclosure generally relate to the production of isoolefin polymers. More particularly, embodiments of the present disclosure relate to separating slurry components in the polymerization of C4-C7 isoolefins.
2. Description of the Related Art
Isoolefin polymers are typically prepared in a slurry polymerization process. Certain slurry processes use methyl chloride as the reaction diluent. Methyl chloride is used for a variety of reasons, including its ability to dissolve the monomers and catalyst but not the polymer product. Methyl chloride also has suitable freezing and boiling points to allow low temperature polymerization and effective separation from the polymer and unreacted monomers.
Following polymerization, the methyl chloride is separated from the polymer product. First, the cold rubber product slurry is heated to prevent plugging in the line between the reactor and the flash tank. In the flash tank, the liquid reaction medium is vaporized. See, for example, U.S. Pat. No. 2,542,559 and RU 2 209 213. The vaporized reaction medium is then cooled and condensed back to a liquid, it is purified, and is recycled to the reactor at the reaction conditions. This is not an energy efficient process.
There are also a number of problems associated with polymerization in methyl chloride. For one, the polymer particles have a tendency to agglomerate with each other in the reactor and collect on the reactor wall, heat transfer surfaces, impeller(s), and agitator(s)/pump(s). The rate of agglomeration increases as reaction temperature rises. The subject of polymer accumulation has been addressed in several patents, such as U.S. Pat. Nos. 2,534,698, 2,548,415, and 2,644,809.
Hydrofluorocarbons (HFC's) have been proposed as alternative diluents. See, for example, WO 02/34794; WO 02/096964; WO 00/04061; U.S. Pat. Nos. 5,624,878; 5,527,870; and 3,470,143. HFC's are environmentally friendly refrigerants because they have a very low (even zero) ozone depletion potential. However, the inefficiencies of the downstream diluent recovery remain the same.
There is a need, therefore, for alternative diluents or blends of diluents to create new polymerization systems that would reduce particle agglomeration in addition to an improved separation process that would improve productivity and efficiency.